Generally, a dewatering agent for sludge, which shows excellent flocculating ability and dewatering ability in a small amount and which is able to be burned up, has been widely used as a flocculant and a dewatering auxiliant against sewage sludge, industrial drainage sludge, and the like.
When an acrylic monomer containing a tertiary amino group is polymerized as it is, since its polymerization does not proceed and a molecular weight does not increase, generally, polymerization has been carried out after the tertiary amino group is quaternized with an alkyl halide and the like or the acrylic monomer is salt formed with a mineral acid and the like.
For instance, as a dewatering agent for sludge, a water-soluble vinyl polymer having a quaternary ammonium group or a tertiary ammonium salt neutralized with a mineral acid and the like has been used. For instance, polymers having an ammonium group quaternized with an alkyl halide such as methyl chloride or ethyl chloride, dimethyl sulfate, diethyl sulfate, and the like are described in Japanese Examined Patent Publication No. 52040/1990, Japanese Examined Patent Publication No. 51141/1988, Japanese Examined Patent Publication No. 48863/1988, Japanese Examined Patent Publication No. 15491/1983, Japanese Unexamined Patent Publication No. 133670/1982, and the like, and a polymer having an ammonium group quaternized with benzyl chloride is described in Japanese Unexamined Patent Publication No. 51899/1982 and the like. Also, in Japanese Examined Patent Publication No. 52040/1990, Japanese Examined Patent Publication No. 15491/1983, Japanese Unexamined Patent Publication No. 49410/1983, Japanese Unexamined Patent Publication No. 47005/1983, Japanese Unexamined Patent Publication No. 133670/1982, and the like, polymers prepared by polymerizing monomers which have been previously salt formed by using a mineral acid such as hydrochloric acid, sulfuric acid or phosphoric acid, or acetic acid are described. However, because the effects of water-soluble vinyl polymers having a quaternary ammonium group or an ammonium group neutralized with a mineral acid and the like are not sufficient for sludge having a difficulty to flocculate and dewater, sludge having a difficulty to flocculate and dewater has been increased in accordance with the high improvement of the treatment for waste water and the like. Then, as a flocculant having excellent dewatering property, which can deal with this increase of sludge, or a flocculant having stable abilities against the change of sludge for the purpose of simplification of working conservation, for instance, it is reported in Japanese Unexamined Patent Publication No. 189400/1989 that a basic substance is added to a cationic polymer whose tertiary amino group is salt formed, and a dewatering agent for sludge made thereof acts as a polymer substantially containing a tertiary amino group. However, a material made by adding a basic substance to a cationic polymer whose tertiary amino group is salt formed does not always show the effects as a polymer containing a tertiary amino group. Moreover, when the neutralization of the material is completely carried out with a basic substance, since the material is changed into a dilute solution of 0.2-% by weight, there was a problem in practicality from the viewpoints of transport, handling and the like.